Growth energetics of an alkaline serine protease-producing strain of Bacillus clausii during continuous cultivation

Glucose-limited chemostats were used to determine the growth yields of biomass of Bacillus clausii PP 473-8 producing an alkaline serine protease Savinase (Novozymes A/S, Bagsvaerd, Denmark) and a low yield of biomass on oxygen was observed. The energy metabolism was investigated further by setting up simple stoichiometric models for growth on glucose and citrate. In order to determine the parameters in the models, a macromolecular biomass composition was determined based on measured values of protein and RNA combined with literature data. From the macromolecular composition of the biomass the theoretical co-factor and building block requirements needed for biomass formation were calculated. Using the stoichiometric models and data for growth on glucose and citrate the amount of ATP needed for biomass synthesis was estimated to 42.0 mmol ATP/gDW, the P/O ratio to 0.68 and the ATP maintenance to 2.93 mmol ATP/gDW/h. From these values it is concluded that the high oxygen consumption compared with other Bacillus species is due to a low efficiency in respiration resulting in a low P/O ratio. Finally, the energetic parameters were estimated for different architectures of the respiratory chain.